The present invention is directed to a method for manufacturing a superconductive composite member by introducing an oxide ceramic superconductive material into an envelope to form an initial composite member, shaping the initial composite member by reducing its cross section to the shape of the final composite member with thermal treatment for recovery and for setting the oxygen concentration. The invention is also directed to a corresponding superconductive composite member.
Superconductive composite members wherein an oxide ceramic superconductive powder is surrounded by an envelope material are known. Examples are disclosed in an article by H. Krauth and A. Szulczyk in METALL, Vol. 43, 1989, pages 418ff. The composite members, such as wires or bands that are also superconductive above the temperature of liquid nitrogen, are manufactured by employing oxide ceramic high-temperature superconductors (HTSC). The materials suitable for this purpose are known per se. Included among them, for example, are phases in the systems of YBaCuO, BiSrCaCuO and TlBaCaCuO.
For manufacturing technical conductors, oxide ceramic powder is filled, for example, into a metal tube and a wire or band is then manufactured by shaping to reduce the cross section of the metal tube or envelope to the desire shape. Subsequently, a thermal treatment is implemented that serves the purpose of producing the continuous, superconductive connection through the HTSC material and the purpose of optimizing the critical current density.
The envelope is usually composed of silver or of silver alloys, because these materials will guarantee the oxygen permeation through the envelope material during the final thermal treatment for setting the optimum oxygen content.
In order to achieve a higher filling density in the manufacture of the composite members, the powder may be pressed into rods or pellets and then filled into the tube or a melt can be filled into the envelope tube. With reference to the theoretical density for the HTSC material, a filling density of approximately 55% is achieved by utilizing powders. Filling densities of approximately 70% are achieved by employing the powder pressed into rods or pellets and a filling density of up to 100% is obtained by filling with a melt. After the shaping of the filled tubes to form the finished composite wire by a drawing or a combination of drawing and rolling steps, the core density of the oxide ceramic superconductive material typically amounts to 65% through 75% of the theoretical density. In the final annealing for setting the superconductive properties, large pores in the core of the HTSC material will occur and will result in a greatly reduced critical current density form, due to the partial melting of the core connected therewith. These pores are, thus, undesirable and should be largely avoided.